This invention relates to a cigarette-lighter, and more particularly, to an electrical heater-element of ceramics, which is incorporated into a plug which is inserted into a socket provided on a front inner car-body, thereby providing the cigarette-lighter.
Conventionally, the plugs making up the cigarette-lighters with sockets provided in cars have been comprised by electrical heater-elements of metallic material.
According to a recent trend, in place of the electrical heater-elements of metallic material, several ceramic materials of the electrical conductive type have been attempted to be employed as the material for constituting the electrical heater-elements due to their heat-resistant characteristics and their oxidization-resistant characteristics. However, the attempts described above for introducing the ceramic materials of the above-described type have not been brought into practical application as yet owing to various problems involved.
For example, there has been already proposed such a plug wherein an outer circumference of a disc-like heater-element of ceramic material, being accommodated inside a heater-casing, is electrically connected to the heater-casing, while a main portion of the heater-element is connected to a metallic electrode coupled to an electric source. However, such a plug of a type as described above has a substantial defect in that since the ceramic materials of the above-described type can be heated up to such a high temperature of 1700.degree. C., the metallic electrode, especially its portion joined with or connected to the heater-element becomes quickly overheated and then is brought into a non conductive state through a continuous energization. In addition, as is well known, since the molding powders of ceramic material are generally difficult to be homogeneously composed, respective compositions of the products are often nonuniform. Therefore, according to such a ceramic heater-element as described above, since the path of the electric current is not specifically defined, the electric current tends to flow for the portions relatively homogeneously composed, thus resulting in the substantial overheat in and around non-homogeneous local portions of the heater-element. Due to the local overheat of the above-described type, the local coefficient of thermal expansion may differ among several portions of the heater-element, whereby cracks or crevices are resultantly caused to be formed. More specifically, a heater having as main portion of a relatively small cross-section is first rendered extraordinarily high in temperature resulting in either the degradation of the material constituting the main portion or cracks in and around the main portion, accordingly.